The objectives of the present research project are to (a) investigate the behavioral contributions made by the cortical and midbrain levels of the auditory nervous system to normal binaural hearing, and (b) to determine the functional significance of bilateral paired structures at the midbrain and cortical levels. Cats will be trained to respond to various auditory cues presented individually to each ear with headphones. The behavioral-ablation method will be used in which cats are tested before and after surgical ablation of specific neural structures. Observed changes in postoperative test performance will be used to derive hypotheses as to the normal functional contributions of specific neural structures. Specific experimental questions to be investigated include: (1) What are the respective roles of the auditory cortex and corpus callosum in those test situations where animals are required to perceptually integrate disparate information presented to the two ears? (2) What are the primary contributions of the midbrain centers (inferior and superior colliculi) to normal binaural hearing? (3) Are there any functional interactions between the midbrain and cortical levels in normal binaural hearing? (4) With respect to normal sound localization, does the auditory cortex provide a critical mechanism which allows animals to perceive the spatial relationships between auditory and other non-auditory stimulus events in the environment?